1 files changed, 177 insertions, 0 deletions
diff --git a/ctdb/include/ctdb_typesafe_cb.h b/ctdb/include/ctdb_typesafe_cb.h
new file mode 100644
index 0000000000..b1f2c5f5b5
--- /dev/null
+++ b/ctdb/include/ctdb_typesafe_cb.h
@@ -0,0 +1,177 @@
+#ifndef CCAN_CAST_IF_TYPE_H
+#define CCAN_CAST_IF_TYPE_H
+
+#if (__GNUC__ >= 3)
+#define HAVE_TYPEOF 1
+#define HAVE_BUILTIN_CHOOSE_EXPR 1
+#define HAVE_BUILTIN_TYPES_COMPATIBLE_P 1
+#endif
+
+#if HAVE_TYPEOF && HAVE_BUILTIN_CHOOSE_EXPR && HAVE_BUILTIN_TYPES_COMPATIBLE_P
+/**
+ * cast_if_type - only cast an expression if test matches a given type
+ * @desttype: the type to cast to
+ * @expr: the expression to cast
+ * @test: the expression to test
+ * @oktype: the type we allow
+ *
+ * This macro is used to create functions which allow multiple types.
+ * The result of this macro is used somewhere that a @desttype type is
+ * expected: if @expr was of type @oktype, it will be cast to
+ * @desttype type.  As a result, if @expr is any type other than
+ * @oktype or @desttype, a compiler warning will be issued.
+ *
+ * This macro can be used in static initializers.
+ *
+ * This is merely useful for warnings: if the compiler does not
+ * support the primitives required for cast_if_type(), it becomes an
+ * unconditional cast, and the @test and @oktype argument is not used.  In
+ * particular, this means that @oktype can be a type which uses
+ * the "typeof": it will not be evaluated if typeof is not supported.
+ *
+ * Example:
+ *	// We can take either an unsigned long or a void *.
+ *	void _set_some_value(void *val);
+ *	#define set_some_value(e)			\
+ *		_set_some_value(cast_if_type(void *, (e), (e), unsigned long))
+ */
+#define cast_if_type(desttype, expr, test, oktype)			\
+__builtin_choose_expr(__builtin_types_compatible_p(typeof(1?(test):0), oktype), \
+			(desttype)(expr), (expr))
+#else
+#define cast_if_type(desttype, expr, test, oktype) ((desttype)(expr))
+#endif
+
+/**
+ * cast_if_any - only cast an expression if it is one of the three given types
+ * @desttype: the type to cast to
+ * @expr: the expression to cast
+ * @test: the expression to test
+ * @ok1: the first type we allow
+ * @ok2: the second type we allow
+ * @ok3: the third type we allow
+ *
+ * This is a convenient wrapper for multiple cast_if_type() calls.  You can
+ * chain them inside each other (ie. use cast_if_any() for expr) if you need
+ * more than 3 arguments.
+ *
+ * Example:
+ *	// We can take either a long, unsigned long, void * or a const void *.
+ *	void _set_some_value(void *val);
+ *	#define set_some_value(expr)					\
+ *		_set_some_value(cast_if_any(void *, (expr), (expr),	\
+ *					    long, unsigned long, const void *))
+ */
+#define cast_if_any(desttype, expr, test, ok1, ok2, ok3)		\
+	cast_if_type(desttype,						\
+		     cast_if_type(desttype,				\
+				  cast_if_type(desttype, (expr), (test), ok1), \
+				  ok2),					\
+		     ok3)
+
+/**
+ * typesafe_cb - cast a callback function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument to hand to the callback function.
+ *
+ * If a callback function takes a single argument, this macro does
+ * appropriate casts to a function which takes a single void * argument if the
+ * callback provided matches the @arg (or a const or volatile version).
+ *
+ * It is assumed that @arg is of pointer type: usually @arg is passed
+ * or assigned to a void * elsewhere anyway.
+ *
+ * Example:
+ *	void _register_callback(void (*fn)(void *arg), void *arg);
+ *	#define register_callback(fn, arg) \
+ *		_register_callback(typesafe_cb(void, (fn), (arg)), (arg))
+ */
+#define typesafe_cb(rtype, fn, arg)			\
+	cast_if_type(rtype (*)(void *), (fn), (fn)(arg), rtype)
+
+/**
+ * typesafe_cb_const - cast a const callback function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument to hand to the callback function.
+ *
+ * If a callback function takes a single argument, this macro does appropriate
+ * casts to a function which takes a single const void * argument if the
+ * callback provided matches the @arg.
+ *
+ * It is assumed that @arg is of pointer type: usually @arg is passed
+ * or assigned to a void * elsewhere anyway.
+ *
+ * Example:
+ *	void _register_callback(void (*fn)(const void *arg), const void *arg);
+ *	#define register_callback(fn, arg) \
+ *		_register_callback(typesafe_cb_const(void, (fn), (arg)), (arg))
+ */
+#define typesafe_cb_const(rtype, fn, arg)				\
+	sizeof((fn)((const void *)0)),					\
+		cast_if_type(rtype (*)(const void *),			\
+			     (fn), (fn)(arg), rtype (*)(typeof(arg)))
+
+/**
+ * typesafe_cb_preargs - cast a callback function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument to hand to the callback function.
+ *
+ * This is a version of typesafe_cb() for callbacks that take other arguments
+ * before the @arg.
+ *
+ * Example:
+ *	void _register_callback(void (*fn)(int, void *arg), void *arg);
+ *	#define register_callback(fn, arg) \
+ *		_register_callback(typesafe_cb_preargs(void, (fn), (arg), int),\
+ *				   (arg))
+ */
+#define typesafe_cb_preargs(rtype, fn, arg, ...)			\
+	cast_if_type(rtype (*)(__VA_ARGS__, void *), (fn), (fn),	\
+		     rtype (*)(__VA_ARGS__, typeof(arg)))
+/**
+ * typesafe_cb_postargs - cast a callback function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument to hand to the callback function.
+ *
+ * This is a version of typesafe_cb() for callbacks that take other arguments
+ * after the @arg.
+ *
+ * Example:
+ *	void _register_callback(void (*fn)(void *arg, int), void *arg);
+ *	#define register_callback(fn, arg) \
+ *		_register_callback(typesafe_cb_postargs(void, (fn), (arg), int),\
+ *				   (arg))
+ */
+#define typesafe_cb_postargs(rtype, fn, arg, ...)			\
+	cast_if_type(rtype (*)(void *, __VA_ARGS__), (fn), (fn),	\
+		     rtype (*)(typeof(arg), __VA_ARGS__))
+/**
+ * typesafe_cb_cmp - cast a compare function if it matches the arg
+ * @rtype: the return type of the callback function
+ * @fn: the callback function to cast
+ * @arg: the (pointer) argument(s) to hand to the compare function.
+ *
+ * If a callback function takes two matching-type arguments, this macro does
+ * appropriate casts to a function which takes two const void * arguments if
+ * the callback provided takes two a const pointers to @arg.
+ *
+ * It is assumed that @arg is of pointer type: usually @arg is passed
+ * or assigned to a void * elsewhere anyway.  Note also that the type
+ * arg points to must be defined.
+ *
+ * Example:
+ *	void _my_qsort(void *base, size_t nmemb, size_t size,
+ *		       int (*cmp)(const void *, const void *));
+ *	#define my_qsort(base, nmemb, cmpfn) \
+ *		_my_qsort((base), (nmemb), sizeof(*(base)), \
+ *			  typesafe_cb_cmp(int, (cmpfn), (base)), (arg))
+ */
+#define typesafe_cb_cmp(rtype, cmpfn, arg)				\
+	cast_if_type(rtype (*)(const void *, const void *), (cmpfn),	\
+		     rtype (*)(const typeof(*arg)*, const typeof(*arg)*))
+		     
+#endif /* CCAN_CAST_IF_TYPE_H */